1. Field of the Invention
The present invention relates to a backlight module and a liquid crystal display (LCD) module using the same, and more particularly, to a backlight module with a reduced light mixing height and an LCD device using the backlight module.
2. Description of Related Art
LCDs are widely applied in a current information product or appliance since they have the advantages of lower prices and mature manufacturing technologies.
An LCD typically uses a passive way to display. Namely, the display requires a backlight module for illumination so that the LCDs generally comprise the backlight modules. The backlight module essentially provides a uniform and sufficient light to an LCD panel and is one of the main optical modules for the LCD. Currently, a light source with LEDs contributes a breakthrough to LCD products, which relatively improves the lighting efficiency to process the efficiency about a half of a cold cathode florescent lamp (CCFL). Also, the LEDs are a low-power self-illuminating light source and typically an auxiliary light source for power-saving products. Therefore, considerable research has included the LEDs in the backlight module of an LCD as a light source.
In a backlight module using a plurality of LEDs as a light source, a mixture of white light is proportioned to the distances between the LED light sources and the light-mixing heights. The different distances between the light sources have the different light-mixing heights. When the distance between the light sources is fixed, a light-mixing unit is used to reduce the light-mixing height. FIG. 1 is a top view of a frame 10 with a typical direct-type light-mixing LED backlight module. FIG. 2 is a schematic side view of the typical backlight module of FIG. 1. As shown in FIG. 1, the frame 10 has a bottom plate 11. The material of the bottom plate 11 can be a metal or polycarbonate (PC). The frame 10 contains a light-mixing unit 13 (FIG. 2) of the backlight module. The bottom plate 11 has a plurality of LEDs 12 in an array arrangement, which emit red, blue and green beams. As shown in FIG. 2, the light-mixing unit 13 is located above the LEDs 12. The red, blue and green beams emitted by the LEDs 12 are mixed in partial areas above the bottom plate 11 to thereby form a white light at, for example, area A, but the result may not be a completely white light. The light-mixing unit 13 is a diffusing mechanism to diffuse the beams emitted by the LEDs 12 so as to expand the lighting angle of the LEDs 12 and to make the light uniform. The light-mixing unit 13 has a diffuser and a transparent plate. The diffuser can be loaded on the transparent plate. The light is delivered from the light-mixing unit 13 to an LCD panel 14 via area B.
In this case, a uniform color light can be generated by meeting a specific diffusing height and using the light-mixing unit 13, after the LEDs 12 have emitted the different colors. The diffusing height required for the uniform color light is about 50 mm and more. Namely, since the lighting angle emitted by the LEDs 12 is not large, a certain distance between the light-mixing unit 13 and the plate 11 is required for completely mixing the different color light emitted by the LEDs 12 and further providing a uniform and good color rendering white light to the LCD panel 14. If the light-mixing unit 13 is very close to the LEDs 12, the lighting angle of the LEDs 12 is not significantly expanded. If the light-mixing unit 13 has two diffusers, the brightness is reduced and the diffusing height cannot be reduced effectively.
As cited, in the aforementioned backlight module, the thickness of which is limited by the distance between the light-mixing unit and the bottom plate, so the entire thickness of the LCD cannot meet the slim-line trend. Therefore, it becomes an important issue to shorten the distance between the light-mixing unit and the bottom plate and to provide a slim LCD to mitigate and/or obviate the aforementioned problems.